Absorbent articles such as diapers which employ relatively thin absorbent cores and which are, therefore, relatively thin products, are desired for numerous reasons. For example, thinner diapers are less bulky to wear and fit better under clothing. They are also more compact in the package, making the diapers easier for the consumer to carry and store. Compactness in packaging also results in reduced distribution costs for the manufacturer and distributor.
The improvement in absorbency provided by incorporation of absorbent gelling materials in absorbent cores has permitted the realization of relatively thin absorbent articles. For example, an absorbent structure wherein hydrogel-forming materials in particulate form are incorporated into fibrous webs is disclosed in Weisman et al.; U.S. Pat. No. 4,610,678; issued Sep. 9, 1986.
Another absorbent core configuration which is useful for use as the absorbent structure in relatively thin absorbent articles is disclosed in U.S. Pat. No. 4,765,780, issued Aug. 23, 1988 to Angstadt. This patent discloses absorbent articles, such as diapers, which have a two layer absorbent core configuration wherein the core comprises an upper primary layer and a lower dusting layer. The primary layer is an airlaid web of hydrophilic fiber material with a substantial amount of absorbent gelling material admixed therewith. The dusting layer comprises hydrophilic fiber material and, preferably, contains no absorbent gelling material.
Another absorbent core configuration is disclosed in Weisman et al., U.S. Pat. No. 4,673,402, issued Jun. 16, 1987. This patent discloses absorbent articles having a dual layer absorbent core. In the dual layer configuration, the core comprises an upper primary layer which is an airlaid web of hydrophilic fiber material, optionally with a small amount of polymeric gelling agent particles admixed therewith. The core also comprises an underlying insert layer which is an airlaid mixture of hydrophilic fiber material and a substantial amount of polymeric gelling agent particles. This insert layer is generally positioned toward the front of the absorbent article such that more than half of the polymeric gelling agent material in the article is found in the front half thereof. Absorbent articles having the particular dual layer configuration of U.S. Pat. No. 4,673,402 can be prepared in the form of especially thin, highly effective, low leakage diaper products.
More recently, absorbent structures have been suggested to provide improved fluid acquisition and distribution in absorbent cores. For example, U.S. Pat. No. 4,935,022, issued Jun. 19, 1990 to Lash et al., discloses disposable absorbent articles comprising a layered absorbent core comprising an upper layer of stiffened, twisted, curled cellulose fibers and from about 3% to 15% by weight, of large particle absorbent gelling material; and a lower layer of stiffened, twisted, curled cellulose fibers and from about 15% to 60%, by weight, of absorbent gelling material. The upper layer serves the principal purpose of acquisition and distribution of bodily fluid discharges. The stiffened, twisted, curled fibers are highly beneficial in this regard. The lower layer is principally for fluid storage.
U.S. Pat. No. 5,217,445, issued to Young et al. on Jun. 8, 1993 discloses absorbent cores comprising an acquisition/distribution layer comprising a web of from about 50% to 100% of chemically stiffened cellulosic fibers and from 0% to about 50% of a binding means. Preferred stiffened fibers are intrafiber crosslinked, the crosslinking occurring while the fibers are in a relatively dehydrated, defibrated, twisted, curled condition. Suitable stiffening agents include polycarboxylates, and are described along with a process of making the stiffened fibers, in U.S. Pat. No. 5,137,537, issued to Herron et al. on Aug. 11, 1992.
Although the foregoing structures provide improved absorbency when incorporated into absorbent articles, it has been found that such cores tend to suffer from absorbent core slumping, cracking (i.e., breaking), and/or roping in processing, storage, and/or use. As a result, the absorption characteristics of the absorbent core are decreased such that leakage of the article incorporating the same occurs. This tendency to slump, crack, and/or rope is more likely as the absorbent core becomes thinner, for example, in the foregoing constructions incorporating absorbent gelling material and/or stiffened, twisted, curled cellulosic fibers. Thin constructions particularly suffer from breakage and slumping which are believed to be due to the presence of stiffened, twisted, curled cellulosic fibers, a relatively high absorbent gelling material concentration, and/or the force typically used in packaging of the absorbent article. Breakage tends to occur along the fold lines typically imparted for packaging of the absorbent articles (e.g., in the crotch region). When such breakage occurs, the transport of fluids throughout the absorbent core is impeded. For example, where substantial breakage occurs along the crotch fold line, the rear portion of the absorbent article tends to be substantially unavailable for fluid absorption. Thus, when the front portion of the article is saturated to its absorption capacity, leakage may occur.
The tendency to slump, crack and/or rope is particularly exaggerated in absorbent cores incorporating acquisition/distribution components comprising stiffened, twisted, curled cellulose fibers such as described in the foregoing patents. On the one hand, the relatively low density of such components makes the component more likely to lose its integrity. In addition, when this component is wetted, the fibers tend to pull apart (spring back). In addition, the acquisition/distribution component tends to separate and/or slip away from other layers of the absorbent core (e.g., the storage layer) such that fluid transport from the acquisition/distribution layer to such other layers is hindered.
It is known to use glues in absorbent articles to improve absorbent core integrity. For example, U.S. Pat. No. 4,573,986, issued to Minetola et al. on Mar. 4, 1986 discloses garments in which the liquid permeable lamina and absorbent core are bonded together in face to face relation with an open pattern of adhesive. Minetola discloses that particular laminae are adhesively secured together with particular patterns, quantities, and types of adhesives to achieve faster absorbency; less absorbent core slumping, cracking and roping; and increased tensile strength without substantially reducing either the softness or overall absorbency of the garment.
While the art has solved some of the problems related to absorbent core integrity of laminated absorbent articles, it has not solved the problems to the extent nor in the manner of the present invention; particularly with respect to the integrity of thin diaper configurations having a relatively high absorbent gelling material concentration, more particularly such thin diapers incorporating an acquisition/distribution layer such as those incorporating the above described chemically stiffened, twisted, curled cellulosic fibers.
The glues used to bond the absorbent core to a chassis component (i.e., topsheet or backsheet) tend to have inadequate adhesion to the cellulose fibers which are typically used in the absorbent core when the absorbent article is subjected to the dynamic motions of the wearer. As a result, the glue tends to be insufficient to maintain the integrity of the absorbent core when absorbent articles incorporating the same are in use. The loss of adhesion and integrity is particularly exaggerated when the article is wetted. For example, when the absorbent gelling material and cellulose fibers typically incorporated into the absorbent core component expand upon wetting, the forces exerted by the expanding absorbent gelling material and cellulose fibers tend to cause a loss of adhesion between the absorbent gelling material, fibers, and the glue.
In addition, when absorbent core/chassis glues are applied in a spray application to form beads and/or spirals for bonding of the laminae, the bonding is relatively localized. Thus, although the amount of glue is relatively great, this method of application leaves a large portion of the absorbent core surface unbonded and free to move.
It is an object of the present invention to provide an absorbent structure having improved dry and wet integrity. Thus it is an object of the present invention to provide an absorbent structure having a reduced tendency to break, slump, and/or rope while dry or wet. Another object of the present invention is to provide absorbent articles in which the absorbent core is enveloped by a continuous mesh of meltblown material. It is a further object of this invention to provide such absorbent articles wherein the absorbent core can acquire fluid rapidly in the region of discharge and transport the fluid over a relatively large proportion of an absorbent core storage area and, additionally, be capable of effectively acquiring and distributing discharged bodily fluid from second or other successive voiding. It is yet another object of this invention to provide absorbent articles which are capable of meeting the objects described above which are of a relatively thin design.